The present invention relates, in general, to a belt drive of an internal combustion engine, and more particularly to a belt drive which has incorporated a starter generator.
Starter generators assume two functions. Firstly, it allows starting of the internal combustion engine, and secondly, it generates electric power during operation of the internal combustion engine. As a consequence of the dual function of the starter generator, the load-carrying run and the non-load carrying run of the belt alternate depending on the mode of operation of the starter generator. All auxiliary units that are typically arranged in the belt drive, such as water pump or servo pump, can be supplied with power by the electric energy produced by the starter generator. It is also conceivable that only the crankshaft pulley and the belt pulley of the starter generator are arranged in the belt drive.
Belt drives of this type may also have incorporated therein a tensioner having two tensioning arms, whereby each tensioning arm is spring-biased against a belt run. German Pat. No. DE 42 43 451 describes such a tensioner for tension means such as belts or chains. This conventional tensioner is not suitable for application in a belt drive with starter generator because both tensioning arms jointly pivot about the rotation axis, without movement relative to one another during operation of the internal combustion engine. Thus, there is a risk that the overall system may severely vibrate as a result of dynamic excitation in the range of the own frequency, thereby impairing the operativeness of the tensioning system.
It would therefore be desirable and advantageous to provide an improved belt drive to obviate prior art shortcomings.
According to one aspect of the present invention, a belt drive of an internal combustion engine, includes a first pulley mounted onto the crankshaft of the internal combustion engine, a second puller mounted to a shaft of a starter generator, a belt looped about the first and second pulleys, and a tensioner having two tensioning arms, each of which loading a belt run of the belt and operating either as load-carrying belt run or non-load carrying belt run, wherein the tensioning arms are disposed to pivot about a rotation axis, and wherein tensioning rollers mounted onto the tensioning arms are spring-biased against the belt, with the tensioning arm disposed respectively upon the load-carrying belt run being urged into a stop position by a force applied by the belt.
According to another feature of the present invention, the belt may be a toothed belt or a V-ribbed belt.
The present invention resolves prior art problems by exploiting the effect that a greater resultant belt force is effective in the load-carrying run of the belt than in the non-load carrying run of the belt. A belt drive according to the present invention is so configured that the increased resultant belt force in the load-carrying belt run urges the associated tensioning arm into the stop position and held there. Thus, the tensioner roller of this tensioning arm works only as deflection roller, whereas the tensioning arm arranged at the non-load carrying belt run operates as directed.
According to another feature of the present invention, the rotation axis of each of the tensioning arms is spaced from the contact area of the tensioning roller upon the belt by a distance which is smaller than a vertical distance between this rotation axis and a tangent which touches the pulleys. When a run of the belt becomes a load-carrying belt run, this run approaches the described tangent and the effective lever arm, which generates in conjunction with the resultant belt force a torque that counteracts the tension spring, decreases. The tensioning arm is thus moved into a dead point position in which no or at best a very slight lever arm is effective for the resultant belt tensioning force. As a consequence, the resultant belt force acts only as tensile force in this tensioning arm. In other words, the rotation axis of the tensioning arm is so positioned in the belt drive that the tensioning arm is pivoted far enough by the resultant belt force so that the resultant belt force extends, at least approximately, in alignment with the tensioning arm.
A belt drive according to the present invention, may include auxiliary units or deflection rollers. Currently preferred is however the incorporation of only the starter generator.
Instead of the described dead point position of the tensioning arm, it may also be conceivable to provide a fixed stop member against which the tensioning arm arranged upon the load-carrying belt run is urged by the resultant belt force and held there. This ensures that the tensioning roller operates also in this variation in the load-carrying belt run as a quasi-rigid deflection roller.
According to another feature of the present invention, both tensioning arms pivot about a common rotation axis. In this way, a space-saving configuration of the overall arrangement is ensured. Of course, the rotation axes of the tensioning arms may also be arranged in spaced-apart relationship.
Suitably, the rotation axes about which the tensioning arms pivot may be arranged within an area that is circumscribed by the belt. The tensioning rollers, on the other hand, may be so disposed as to be arranged outside this area that is circumscribed by the belt. In this way, a tension spring may be provided between both tensioning arms for urging the tensioning arms toward one another.